Lesson Overview

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Lesson Overview

• 14.3 Studying the Human Genome

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Manipulating DNA

• DNA is a huge moleculeeven the smallest human
  chromosome contains nearly 50 million base pairs.
  Manipulating such large molecules is extremely
  difficult.
• In the 1970s, scientists found that they could
  read the base sequences in DNA by using natural
  enzymes to cut, separate, and replicate DNA base
  by base.

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Cutting DNA

• Nucleic acids are chemically different from
  other macromolecules such as proteins and
  carbohydrates. This difference makes DNA
  relatively easy to extract from cells and
  tissues.
• DNA molecules from most organisms are much too
  large to be analyzed, so they must first be cut
  into smaller pieces.
• Many bacteria produce restriction enzymes that
  cut DNA molecules into precise pieces, called
  restriction fragments that are several hundred
  bases in length.
• Of the hundreds of known restriction enzymes,
  each cuts DNA at a different sequence of
  nucleotides.

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Cutting DNA

• For example, the EcoRI restriction enzyme
  recognizes the base sequence GAATTC.
• It cuts each strand between the G and A bases,
  leaving single-stranded overhangs, called sticky
  ends, with the sequence AATT.
• The sticky ends can bond, or stick, to a DNA
  fragment with the complementary base sequence.

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Separating DNA

• Once DNA has been cut by restriction enzymes,
  scientists can use a technique known as gel
  electrophoresis to separate and analyze the
  differently sized fragments.

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Separating DNA

• A mixture of DNA fragments is placed at one end
  of a porous gel.
• When an electric voltage is applied to the gel,
  DNA moleculeswhich are negatively chargedmove
  toward the positive end of the gel.
• The smaller the DNA fragment, the faster and
  farther it moves.
• The result is a pattern of bands based on
  fragment size.
• Specific stains that bind to DNA make these
  bands visible.
• Researchers can remove individual restriction
  fragments from the gel and study them further.

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The Human Genome Project

• What were the goals of the Human Genome Project,
  and what have we
• learned so far?
• The Human Genome Project was a 13-year,
  international effort with the
• main goals of sequencing all 3 billion base pairs
  of human DNA and
• identifying all human genes.
• The Human Genome Project pinpointed genes and
  associated
• particular sequences in those genes with numerous
  diseases and
• disorders. It also identified about 3 million
  locations where single-base
• DNA differences occur in humans.

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Lesson Overview

• 15.1 Selective
• Breeding

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Selective Breeding

• The differences among breeds of dogs are great.
• Where did these differences come from?
• Humans use selective breeding to produce animals
  with certain desired traits.
• Selective breeding allows only those animals
  with wanted characteristics to produce the next
  generation. For thousands of years, weve
  produced new varieties of cultivated plants and
  nearly all domestic animals by selectively
  breeding for particular traits.
• Native Americans selectively bred teosinte, a
  wild grass native to central Mexico, to produce
  corn, a far more productive and nutritious plant.
  Corn is now one of the worlds most important
  crops.
• There are two common methods of selective
  breedinghybridization and inbreeding.

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Hybridization

• American botanist Luther Burbank developed more
  than 800 varieties of plants using selective
  breeding methods.
• One method Burbank used was hybridization,
  crossing dissimilar individuals to bring together
  the best of both organisms.
• Hybridsthe individuals produced by such
  crossesare often hardier than either of the
  parents.
• Many of Burbanks hybrid crosses combined the
  disease resistance of one plant with the
  food-producing capacity of another. The result
  was a new line of plants that had the traits
  farmers needed to increase food production.
• July Elberta peaches, for example, are among
  Burbanks most successful varieties.

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Inbreeding

• To maintain desirable characteristics in a line
  of organisms, breeders often use inbreeding, the
  continued breeding of individuals with similar
  characteristics.
• The many breeds of dogs are maintained using
  inbreeding, ensuring that the characteristics
  that make each breed unique are preserved.
• Although inbreeding is useful in preserving
  certain traits, it can be risky.
• Most of the members of a breed are genetically
  similar, which increases the chance that a cross
  between two individuals will bring together two
  recessive alleles for a genetic defect.

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Increasing Variation

• When scientists manipulate the genetic makeup of
  an organism, they are using biotechnology.
• Biotechnology is the application of a
  technological process, invention, or method to
  living organisms.
• Selective breeding is one form of biotechnology
  important in agriculture and medicine, but there
  are many others.

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Bacterial Mutations

• Mutations occur spontaneously, but breeders can
  increase the mutation rate of an organism by
  using radiation or chemicals.
• Many mutations are harmful to the organism, but
  breeders can often produce a few
  mutantsindividuals with mutationswith useful
  characteristics that are not found in the
  original population.
• Certain strains of oil-digesting bacteria are
  effective for cleaning up oil spills, and
  scientists are currently working to produce
  bacteria that can clean up radioactive substances
  and metal pollution in the environment.

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Polyploid Plants

• Drugs that prevent the separation of chromosomes
  during meiosis are very useful in plant breeding.
  These drugs can produce cells that have many
  times the normal number of chromosomes.
• Plants grown from these cells are called
  polyploid because they have many sets of
  chromosomes.
• Polyploidy is usually fatal in animals, but
  plants are much better at tolerating extra sets
  of chromosomes.
• Polyploidy can quickly produce new species of
  plants that are larger and stronger than their
  diploid relatives.
• A number of important crop plants, including
  bananas, have been produced in this way.

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Polyploid Plants
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Lesson Overview

• 15.2 Recombinant DNA

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Genetic Engineering Summary

• Cut DNA - gene of interest and vector - using
  same restriction enzymes
• Separate the DNA - using gel electrophoresis
• Isolate the gene of interest - using southern
  blot
• Copy the gene - using polymerase chain reaction
  (PCR)
• Create recombinant DNA - insert copies into
  vector DNA (plasmid)
• Insert recombinant DNA - into new organism
• Clone DNA - allow cell to copy gene of interest
  each time it divides
• Screen cells - use antibiotics to destroy cells
  without the gene of interest

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Finding Genes- Southern Blot Analysis

• To find a specific gene, a complementary base
  sequence is used to attract an mRNA that
  contains the desired gene and would bind to that
  sequence by base pairing.
• This complementary sequence is called a probe.
• This method is called Southern blotting, after
  its inventor, Edwin Southern.

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Polymerase Chain Reaction

• Once biologists find a gene, a technique known
• as polymerase chain reaction (PCR) allows
• them to make many copies of it.
• A piece of DNA is heated, which separates its two
  strands.
• 2. At each end of the original piece of DNA, a
  biologist adds a short piece of DNA that
  complements a portion of the sequence.
• These short pieces are known as primers because
  they prepare, or prime, a place for DNA
  polymerase to start working.

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Polymerase Chain Reaction

• 3. DNA polymerase copies the region between the
  primers. These copies then serve as templates to
  make more copies.
• 4. In this way, just a few dozen cycles of
  replication can produce billions of copies of the
  DNA between the primers.

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Creating Recombinant DNA

• A gene from one organism can be attached to the
  DNA of another organism.
• Restriction enzymes cut DNA at specific
  sequences, producing sticky ends, which are
  single-stranded overhangs of DNA.
• If two DNA molecules are cut with the same
  restriction enzyme, their sticky ends will bond
  to a DNA fragment that has the complementary base
  sequence. DNA ligase then joins the two
  fragments.
• The resulting molecules are called recombinant
  DNA.

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Combining DNA Fragments

• Recombinant-DNA technologyjoining together DNA
  from two or more sourcesmakes it possible to
  change the genetic composition of living
  organisms.
• By manipulating DNA in this way, scientists can
  investigate the structure and functions of genes.

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Plasmids and Genetic Markers

• In addition to their own large chromosomes, some
  bacteria contain small circular DNA molecules
  known as plasmids.
• Joining DNA to a plasmid, and then using the
  recombinant plasmid to transform bacteria,
  results in the replication of the newly added DNA
  along with the rest of the cells genome.
• Bacteria can be transformed using recombinant
  plasmids.
• Scientists can insert a piece of DNA into a
  plasmid if both the plasmid and the target DNA
  have been cut by the same restriction enzymes to
  create sticky ends.

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Plasmid DNA Transformation Using Human Growth
Hormone
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Copying the Recombinant DNA

• The new combination of genes is then returned to
  a bacterial cell, which replicates the
  recombinant DNA over and over again and produces
  human growth hormone.

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Screening for the gene of interest

• The recombinant plasmid has a genetic marker,
  such as a gene for antibiotic resistance. A
  genetic marker is a gene that makes it possible
  to distinguish bacteria that carry the plasmid
  from those that dont.
• After transformation, the bacteria culture is
  treated with an antibiotic. Only those cells that
  have been transformed survive, because only they
  carry the resistance gene.

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Transgenic Organisms

• The universal nature of the genetic code makes
  it possible to construct organisms that are
  transgenic, containing genes from other species.
• Genetic engineers can now produce transgenic
  plants, animals, and microorganisms.

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Transgenic Plants

• Many plant cells can be transformed using
  Agrobacterium.
• In nature this bacterium inserts a small DNA
  plasmid that produces tumors in a plants cells.
• Scientists can deactivate the plasmids
  tumor-producing gene and replace it with a piece
  of recombinant DNA. The recombinant plasmid can
  then be used to infect and transform plant cells.
• The transformed cells can be cultured to produce
  healthy adult plants.

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Transgenic Plants Transforming a Plant with
Agrobacterium
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Cloning

• A clone is a member of a population of
  genetically identical cells produced from a
  single cell.
• The technique of cloning uses a single cell from
  an adult organism to grow an entirely new
  individual that is genetically identical to the
  organism from which the cell was taken.Clones
  of animals were first produced in 1952 using
  amphibian tadpoles.
• In 1997, Scottish scientist Ian Wilmut announced
  that he had produced a sheep, called Dolly, by
  cloning.

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Cloning

• Animal cloning uses a procedure called nuclear
  transplantation.
• The process combines an egg cell with a donor
  nucleus to produce an embryo.
• First, the nucleus of an unfertilized egg cell
  is removed.
• Next, the egg cell is fused with a donor cell
  that contains a nucleus,
• taken from an adult.
• The resulting diploid egg develops into an
  embryo, which is then
• implanted in the uterine wall of a foster
  mother, where it develops until birth.
• Cloned cows, pigs, mice, and even cats have
  since been produced using similar techniques.

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Cloning AnimalsNuclear Transplantation
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Lesson Overview

• 15.3 Applications of Genetic Engineering

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Agriculture and Industry

• Almost everything we eat and much of what we
  wear come from living organisms.
• Researchers have used genetic engineering to try
  to improve the products we get from plants and
  animals.
• Genetic modification could lead to better, less
  expensive, and more nutritious food as well as
  less harmful manufacturing processes.

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GM Crops

• Since their introduction in 1996, genetically
  modified (GM) plants have become an important
  component of our food supply.
• One genetic modification uses bacterial genes
  that produce a protein known as Bt toxin.
• This toxin is harmless to humans and most other
  animals, but enzymes in the digestive systems of
  insects convert Bt to a form that kills the
  insects.
• Plants with the Bt gene do not have to be
  sprayed with pesticides.
• In addition, they produce higher yields of
  crops.
• Other useful genetic modifications include
  resistance to herbicides, which are chemicals
  that destroy weeds, and resistance to viral
  infections.

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GM Animals

• Transgenic animals are becoming more important
  to our food supply.
• About 30 percent of the milk in U.S. markets
  comes from cows that have been injected with
  hormones made by recombinant-DNA techniques to
  increase milk production.
• Pigs can be genetically modified to produce more
  lean meat or high levels of healthy omega-3
  acids.
• Using growth-hormone genes, scientists have
  developed transgenic salmon that grow much more
  quickly than wild salmon.

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GM Animals

• Scientists in Canada combined spider genes into
  the cells of lactating goats. The goats began to
  produce silk along with their milk.
• The silk can be extracted from the milk and
  woven into a thread that can be used to create a
  light, tough, and flexible material.
• Scientists are working to combine a gene for
  lysozymean antibacterial protein found in human
  tears and breast milkinto the DNA of goats.
• Milk from these goats may help prevent
  infections in young children who drink it.

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GM Animals

• Researchers hope that cloning will enable them
  to make copies of transgenic animals, which would
  increase the food supply and could help save
  endangered species.
• In 2008, the U.S. government approved the sale
  of meat and milk from cloned animals.
• Cloning technology could allow farmers to
  duplicate the best qualities of prize animals
  without the time and complications of traditional
  breeding.

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Preventing Disease

• Golden rice is a GM plant that contains
  increased amounts of provitamin A, also known as
  beta-carotenea nutrient that is essential for
  human health. Two genes engineered into the rice
  genome help the grains produce and accumulate
  beta-carotene. Provitamin A deficiencies
  produce serious medical problems, including
  infant blindness. There is hope that provitamin
  Arich golden rice will help prevent these
  problems.
• Other scientists are developing transgenic
  plants and animals that produce human antibodies
  to fight disease.

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Preventing Disease

• In the future, transgenic animals may provide us
  with an ample supply of our own proteins.
• Several laboratories have engineered transgenic
  sheep and pigs that produce human proteins in
  their milk, making it easy to collect and refine
  the proteins.
• Many of these proteins can be used in disease
  prevention.

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Medical Research

• Transgenic animals are often used as test
  subjects in medical research. They can simulate
  human diseases in which defective genes play a
  role.
• Scientists use models based on these simulations
  to follow the onset and progression of diseases
  and to construct tests of new drugs that may be
  useful for treatment.
• This approach has been used to develop models
  for disorders like Alzheimers disease and
  arthritis.

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Treating Disease

• Recombinant-DNA technology can be used to make
  important proteins that could prolong and even
  save human lives.
• For example, human growth hormone, which is used
  to treat patients suffering from pituitary
  dwarfism, is now widely available because it is
  mass-produced by recombinant bacteria.
• Other products now made in genetically
  engineered bacteria include insulin to treat
  diabetes, blood-clotting factors for
  hemophiliacs, and potential cancer-fighting
  molecules such as interleukin-2 and interferon.

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Treating Disease

• Gene therapy is the process of changing a gene
  to treat a medical disease or disorder.
• In gene therapy, an absent or faulty gene is
  replaced by a normal, working gene.
• This process allows the body to make the protein
  or enzyme it needs, which eliminates the cause of
  the disorder.

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Treating Disease One Example of Gene Therapy

• To deliver therapeutic genes to target cells
  researchers engineer a virus that cannot
  reproduce or cause harm.
• The DNA containing the therapeutic gene is
  inserted into the modified virus.

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Treating Disease One Example of Gene Therapy

• The patients cells are then infected with the
  genetically engineered virus.
• In theory the virus will insert the healthy gene
  into the target cell and correct the defect.

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Treating Disease

• Gene therapy can be risky.
• In 1999, 18-year-old Jesse Gelsinger volunteered
  for a gene therapy experiment designed to treat a
  genetic disorder of his liver. He suffered a
  massive reaction from the viruses used to carry
  genes into his liver cells, and he died a few
  days later.
• For gene therapy to become an accepted
  treatment, we need more reliable ways to insert
  working genes and to ensure that the DNA used in
  the therapy does no harm.

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Genetic Testing

• Genetic tests are now available for diagnosing
  hundreds of disorders.
• Some genetic tests search for changes in cutting
  sites of restriction enzymes, while others use
  PCR to detect differences between the lengths of
  normal and abnormal alleles.

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Examining Active Genes

• The same genes are not active in every cell. By
  studying which genes are active and which are
  inactive in different cells, scientists can
  understand how the cells function normally and
  what happens when genes dont work as they
  should.
• Scientists use DNA microarray technology to
  study hundreds or even thousands of genes at once
  to understand their activity levels.

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Personal Identification

• DNA fingerprinting can be used to identify
  individuals by analyzing these sections of DNA
  that may have little or no function but that vary
  widely from one individual to another.
• DNA samples can be obtained from blood, sperm,
  or tissueeven from a hair strand if it has
  tissue at the root.

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Forensic Science

• The precision and reliability of DNA
  fingerprinting has revolutionized forensicsthe
  scientific study of crime scene evidence.
• DNA fingerprinting has helped solve crimes,
  convict criminals, and even overturn wrongful
  convictions.
• To date, DNA evidence has saved more than 110
  wrongfully convicted prisoners from death
  sentences.
• DNA forensics is used in wildlife conservation
  as well.

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Establishing Relationships

• When genes are passed from parent to child,
  genetic recombination scrambles the molecular
  markers used for DNA fingerprinting, so ancestry
  can be difficult to trace.
• The Y chromosome, however, never undergoes
  crossing over, and only males carry it.
  Therefore, Y chromosomes pass directly from
  father to son with few changes.
• Y-chromosome analysis has helped researchers
  settle longstanding historical questions such
  asDid President Thomas Jefferson father the
  child of a slave?
• DNA testing showed that descendants of the son
  of Sally Hemings, a slave on Jeffersons Virginia
  estate, carried his Y chromosome.
• This result suggests Jefferson was the childs
  father, although the Thomas Jefferson Foundation
  continues to challenge that conclusion.

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Establishing Relationships

• Similarly, the small DNA molecules found in
  mitochondria are passed, with very few changes,
  from mother to child in the cytoplasm of the egg
  cell.
• Because mitochondrial DNA (mtDNA) is passed
  directly from mother to child, your mtDNA is the
  same as your mothers mtDNA, which is the same as
  her mothers mtDNA.
• This means that if two people have an exact
  match in their mtDNA, then there is a very good
  chance that they share a common maternal
  ancestor.

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Lesson Overview

• 15.4 Ethics and Impacts of Biotechnology

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Safety of Transgenics

• Are GM foods safe?
• Careful studies of such foods have provided no
  scientific support for concerns about their
  safety, and it does seem that foods made from GM
  plants are safe to eat.

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Pros of GM Foods

• Farmers choose GM crops because they produce
  higher yields, reducing the amount of land and
  energy that must be devoted to agriculture and
  lowering the cost of food for everyone.
• Insect-resistant GM plants need little, if any,
  insecticide to grow successfully, reducing the
  chance that chemical residues will enter the food
  supply and lessening damage to the environment.
• Careful studies of GM foods have provided no
  scientific support for concerns about their
  safety, and it does seem that foods made from GM
  plants are safe to eat.

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Cons of GM Foods

• Critics point out that no long-term studies have
  been made of the hazards these foods might
  present.
• Some worry that the insect resistance engineered
  into GM plants may threaten beneficial insects,
  killing them as well as crop pests.
• Others express concerns that use of plants
  resistant to chemical herbicides may lead to
  overuse of these weed-killing compounds.
• Another concern is that the patents held on GM
  seeds by the companies that produce them may
  prove costly enough to force small farmers out of
  business, especially in the developing world.

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Cons of GM Foods

• In the United States, current federal
  regulations treat GM foods and non-GM foods
  equally.
• GM foods are not required to undergo special
  safety testing before entering the market.
• No additional labeling is required to identify a
  product as genetically modified unless its
  ingredients are significantly different from its
  conventional counterpart.
• The possibility that meat from GM animals may
  soon enter the food supply has heightened
  concerns about labeling. As a result, some states
  have begun to consider legislation to require the
  labeling of GM foods, thereby providing consumers
  with an informed choice.

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Ethics of the New Biology

• Should genetic modifications to humans and other
  organisms be closely regulated?
• Just because we have the technology to modify an
  organisms characteristics, are we justified in
  doing so?

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Ethics of the New Biology

• If human cells can be manipulated to cure
  disease, should biologists try to engineer taller
  people or change their eye color, hair texture,
  sex, blood group, or appearance?
• What will happen to the human species when we
  gain the opportunity to design our bodies or
  those of our children?
• What will be the consequences if biologists
  develop the ability to clone human beings by
  making identical copies of their cells?
• These are questions with which society must come
  to grips.

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Ethics of the New Biology

• The goal of biology is to gain a better
  understanding of the nature of life.
• As our knowledge increases, however, so does our
  ability to manipulate the genetics of living
  things, including ourselves.
• In a democratic nation, all citizens are
  responsible for ensuring that the tools science
  has given us are used wisely.
• We should all be prepared to help develop a
  thoughtful and ethical consensus of what should
  and should not be done with the human genome.